In the process of manufacturing silicon or other semiconductor microchips, light is generally directed through a reticle mask to etch circuits into a silicon wafer. The presence of dirt, dust, smudges or other foreign matter on the surfaces of the reticle mask or the silicon wafer is highly undesirable and adversely affects the resulting circuits. As a result, the reticles and the silicon wafers are necessarily inspected before use. One common inspection technique is for a human inspector to visually examine each surface under intense light and magnification. Debris that is smaller than can be visually detected by the human eye, however, impairs the resulting microchips.
Laser inspection systems therefore have been developed for inspecting the surface of silicon wafers to accurately detect small particles. In these conventional laser inspection systems, light is both specularly reflected and scattered from the surface of an article. The specularly reflected light and the scattered light are both indicative of the presence of particles or flaws on the surface of the article. The light specularly reflected from the surface and the light scattered from the surface are collected and separately relayed to photodetectors such as a photomultiplier tube ("PMT") or a charge coupled device ("CCD").
Several laser inspection systems have been developed which provide various types collectors, such as fiber optic bundles, spherical or parabolic mirrors, elongated lenses, and light pipes, for collecting the light and separately relaying the light to photodetectors. Examples of such systems may be seen in U.S. Pat. No. 4,875,780 by Moran et al. entitled "Method and Apparatus for Inspecting Reticles"; U.S. Pat. No. 4,795,911 by Kohno et al. entitled "Surface Examining Apparatus For Detecting The Presence of Foreign Particles on the Surface"; U.S. Pat. No. 4,630,276 by Moran entitled "Compact Laser Scanning System"; U.S. Pat. No. 4,601,576 by Galbraith entitled "Light Collector For Optical Contaminant And Flaw Detector"; U.S. Pat. No. 4,378,159 by Galbraith entitled "Scanning Contaminant And Defect Detector"; U.S. Pat. No. 4,376,583 by Alford et al. entitled "Surface Inspection Scanning System"; and U.S. Pat. No. 4,360,275 by Louderback entitled "Device for Measurement of Optical Scattering". The collectors of these systems, however, are often bulky and awkward for installation into commercial laser inspection machines and are often inefficient in collecting portions of the light.
Thus, there is a need for a particle detection system which compactly and efficiently collects the light specularly reflected and scattered from the surface of an article and focuses the light into a photodetector.